David Wagner insists Alexander Nubel did not intend to do harm to Mijat Gacinovic with his horror challenge in Schalke's 1-0 win over Eintracht Frankfurt.
The Schalke goalkeeper was shown a 66th-minute red card for a wild lunge with his foot that caught his opponent high on the chest.
Head coach Wagner accepted referee Felix Zwayer had little option other than to give Nubel his marching orders but defended his captain.
"Alexander Nubel wasn't trying to catch Mijat Gacinovic when he was sent off, but just arrived too late," Wagner said in quotes reported by Schalke's official website.
"It obviously looks really bad. The referee's decision was definitely correct. Markus Schubert was great after coming on, as was Juan Miranda."
Gacinovic later posted on Instagram to show the result of the challenge, with stud marks visible across the midfielder's chest.
Schalke's win, which was sealed by Benito Raman's effort in the 53rd minute, leaves them fourth in the table and five points adrift of leaders RB Leipzig.